European stock markets were volatile Monday despite the European Central Bank saying it intended to buy up government debt.

European Commission spokesperson Ollie Bailly said Monday that the measures taken by the European Central Bank should calm investors' jitters.

"All of the messages that came over the weekend from the G20, the G7, the different member states and the European Central Bank go in the right direction, in the good, in the same direction, and send a strong message of confidence to the markets and to the key players," Bailly said.

The European Central Bank, or ECB, announced Sunday that it would buy Spanish and Italian bonds in order to stabilize the markets. The move was designed to allay fears that two of Europe’s largest economies might default on their debts.

Already, the eurozone has bailed out three of its member nations -- Greece, Ireland and Portugal - to prevent them from defaulting.

S&P lists 5 pillars in its Sovereign Rating Framework as:

Institutional effectiveness and political risks, reflected in the political score

Economic structure and growth prospects, reflected in the economic score

External liquidity and international investment position, reflected in the external score

Fiscal performance and flexibility, as well as debt burden, reflected in the fiscal score

Monetary flexibility, reflected in the monetary score

(Source: Standard & Poor's Sovereign Rating Framework)

On Monday, dealers said the ECB began buying Italian and Spanish debt as soon as European bond markets opened.

Initially the plan seemed to be working. Yields on 10-year Italian and Spanish bonds fell dramatically, and the euro rose against the dollar.

Nick Parsons, an economist at National Australia Bank, said the ECB had made the right move.

"It has been an absolutely critical decision, and I think we are going to have to see much more of this in the future if we are going to continue this spread tightening," Parsons said.

But the gains were unstable; European markets slipped back in the afternoon.

Analysts say part of the problem is that investors are worried about the U.S. economy. On Friday, the U.S. credit rating was downgraded, and on Monday, Wall Street stocks tumbled.

The U.S. is the world’s largest economy, and the state of its finances has global repercussions. Shares in Japan, China, Taiwan and South Korea also plunged Monday.

Analysts say the problem in Europe is domestic as well. The ECB and European leaders still, they say, have not made a concrete plan about what they will do next to cope with the European sovereign debt crisis and stagnating economies.

Vanessa Rossi from London’s Chatham House is an expert on the European economy.

She says, in the first place, it is not clear that the ECB has enough funds to keep Spain and Italy clear of the brink.

“I would have serious concerns that the amount of funding they would need to be able to make a real impact there will perhaps be more than the resources they wish to allocate,” Rossi said.

Government policy, she says, is not aimed at creating economic growth, and nations are relying on exports to keep their economies afloat.

"The difficulty is that governments virtually have no fire power left to provide any stimulus," Rossi said.

On Friday, Italian Prime Minister Silvio Berlusconi announced plans to balance the country's budget by 2013 - a year earlier than planned - while Spain has also promised to speed up cost-saving measures.